1. Field of Invention
This invention is concerned with apparatus for positioning an object in three-dimensional space and, more particularly, with such an apparatus utilizing multiple piezoelectric elements to create the positioning motion.
2. Description of the Prior Art
There is often a need to move an object with small but controlled motions. For example, it may be necessary to move a lens or light source to read from or write to an optical disk in orthogonal directions toward and away from the disk and along a radial of the disk in opposite directions. It is known to utilize a moving coil actuator to accomplish the aforementioned task. Such actuators utilize delicate and complex mechanisms, including compound spring suspensions, rigid coil assemblies, rare earth permanent magnets, and pole pieces. Such actuators undesirably possess multi-mode mechanical resonances frequently causing instabilities in high performance servo use. Further, the magnetic field present in such actuators may interfere with the magneto-optic properties of the recording and reading of such optical disks.
It is also known to utilize piezoelectric elements for such control as illustrated in U.S. Pat. No. 4,475,179 issued Oct. 2, 1984, and particularly as illustrated in FIG. 2 thereof, which shows a set of four piezoelectric element pairs (bimorphs) for moving an object in the Y directions toward and away from an optical disk and in the X direction radially along the surface of the optical disk. What is not illustrated in FIG. 2 but what must of necessity be present, since the action of a piezoelectric bimorph is to bend, is that there is also motion in directions mutually orthogonal to the illustrated X direction and Y direction thereof, i.e. toward and away from support 52.